The present invention relates to a wheelchair having an electric drive, and steerable wheels which may be steered by means of a joystick via an electro-mechanical control device. The steerable wheels may be pivotally moved into a lateral angular position to enable the wheelchair to be driven in a straight line or along a curved path.
In known wheelchairs the steerable wheels may be swivelled relatively hard to one side or the other in order to provide a small turning circle (bend radius). However, a large lateral lock of the steerable wheels could lead to an accident if it were applied fully when the wheelchair was travelling at too high a speed, since the inertia (rotary mass) of the wheelchair containing the passenger and the centrifugal force acting on the wheelchair, may be too large to follow the curved path of the steered wheels, and in such a case the wheelchair tips over. For this reason stops have been provided on the chassis to limit the lateral deflection (lateral lock) of the steerable wheels. This has the disadvantage of producing an undesirably large turning circle. Also, with a steering speed which is proportional with the travelling speed of the vehicle, the tilting moment with full steering lock still occurs but is only delayed in time.
It is an object of the invention to develop a wheelchair having a steering device such that the maximum possible lateral lock of the steering wheels is so controlled and limited in dependence upon the travelling speed and that the moment of inertia (rotary mass) of the turning movement of the wheelchair (the lateral deflection of the steering wheels) is proportional, so that the wheelchair follows the turning movement of the steering wheels at any speed and hence the centrifugal force does not cause the wheelchair to tip over.